The present invention relates to an eddy current apparatus comprising a stator assembly, and a rotor assembly revolving with respect to the stator assembly about an axis of rotation, one of the two assemblies including inductor coils whose respective axes are parallel to the axis of rotation and distributed at regular intervals along a circle centred on the axis of rotation, each coil being traversed by a cylindrical pole core, one end of which is provided with a pole shoe of larger cross-section, and the other of the two assemblies including at least one armature disc situated facing the pole shoes with interposition of a gap, in which, in relation to the direction of travel of the armature disc past the pole shoes, each pole shoe offers to the armature disc an area which is larger in front than to the rear of the radial plane passing through the axis of rotation and through the axis of the corresponding coil.
It relates, in particular, but not exclusively to eddy current retarders in which the inductor coils form part of the stator assembly, and the armature disc forms part of the rotor assembly.
The pole shoes fulfill several functions:
they leave a certain distance between the coils and the armature so as to limit the magnetic forces of axial attraction which are exerted on the armature;
they ensure good distribution of the magnetic flux in the armature and hence efficient generation of eddy currents;
they also have a mechanical role of holding in place and protecting the coils and/or the pole cores.
The benefit in providing for the pole shoes to offer to the armature disc a larger area in front than to the rear of the radial plane passing through the polar axis has been demonstrated in French Patent No. 2,574,228 or U.S. Pat. No. 4,668,886. This makes it possible to attain higher braking torques by virtue of lesser magnetic saturation on the rear side of the shoes as compared with the conventional configuration in which the shoes are placed symmetrically with respect to the aforesaid radial plane.
An object of the present invention is to further increase the torques which the apparatus is capable of generating by producing eddy currents in the armature.